add SimpleSchemeConstraint.sol (#803)

* add SimpleSchemeConstraint.sol

* test coverage

* bump v to rc.48

contracts/schemes/SchemeConstraints.sol

@@ -6,6 +6,9 @@ import "../controller/Avatar.sol";
 contract SchemeConstraints {
 
     address[] public contractsWhiteList;
+    //descriptionHash can be used to add detalis description of the constraints.
+    //e.g it can be ipfs hash of the contractsWhiteList abis +names.
+    string public descriptionHash;
 
    /*
     * @dev isAllowedToCall should be called upon a proposal execution.

contracts/schemes/SimpleSchemeConstraints.sol

@@ -0,0 +1,69 @@
+pragma solidity 0.5.17;
+pragma experimental ABIEncoderV2;
+
+import "./SchemeConstraints.sol";
+
+//a simple genericSchemeMultiCall constraint which put constraints only on white listed contracts to call.
+
+contract SimpleSchemeConstraints is SchemeConstraints {
+
+    mapping(address=>bool) public contractsWhiteListMap;
+    bool public initialized;
+
+    /* @dev initialize
+     * @param _contractsWhiteList the contracts the scheme is allowed to interact with
+     * @param _descriptionHash can be used to add detalis description of the constraints.
+     */
+    function initialize(
+        address[] calldata _contractsWhiteList,
+        string calldata _descriptionHash
+    )
+    external {
+        require(!initialized, "cannot initialize twice");
+        initialized = true;
+        for (uint i = 0; i < _contractsWhiteList.length; i++) {
+            contractsWhiteListMap[_contractsWhiteList[i]] = true;
+        }
+        contractsWhiteList = _contractsWhiteList;
+        descriptionHash = _descriptionHash;
+    }
+
+    /*
+     * @dev isAllowedToCall should be called upon a proposal execution.
+     * @param _contractsToCall the contracts to be called
+     * @return bool value true-allowed false not allowed
+     */
+    function isAllowedToCall(
+        address[] calldata _contractsToCall,
+        bytes[] calldata,
+        uint256[] calldata,
+        Avatar
+    )
+    external
+    returns(bool)
+    {
+        for (uint i = 0; i < _contractsToCall.length; i++) {
+            require(contractsWhiteListMap[_contractsToCall[i]], "contract not whitelisted");
+        }
+        return true;
+    }
+
+    /*
+     * @dev isAllowedToPropose should be called upon a proposal submition.
+     * @param _contractsToCall the contracts to be called
+     * @return bool value true-allowed false not allowed
+     */
+    function isAllowedToPropose(
+        address[] calldata _contractsToCall,
+        bytes[] calldata,
+        uint256[] calldata,
+        Avatar)
+    external
+    returns(bool)
+    {
+        for (uint i = 0; i < _contractsToCall.length; i++) {
+            require(contractsWhiteListMap[_contractsToCall[i]], "contract not whitelisted");
+        }
+        return true;
+    }
+}